Which is harder, 1018 or 4140 steel?

Which is Harder, 1018 or 4140 Steel?

When selecting steel for a project, hardness is a key property to consider, especially for applications involving wear resistance, machining, or structural integrity. SAE-AISI 1018 and SAE-AISI 4140 are two common steel grades with distinct properties due to their differing compositions and processing methods.

At Gangsteel, a trusted ASTM A 36 steel plate supplier, we often address questions about material properties to help clients choose the right steel, even though our focus is on structural grades like ASTM A36/A36M. This article compares the hardness of 1018 and 4140 steel, exploring their compositions, heat treatment, and applications to determine which is harder.

Understanding Hardness in Steel

Hardness refers to a material’s ability to resist deformation, scratching, or indentation, often measured using the Brinell (HB), Rockwell (HRC or HRB), or Vickers scales. Steel hardness is influenced by:

• Carbon Content: Higher carbon increases hardness but reduces ductility.
• Alloying Elements: Elements like chromium and molybdenum enhance hardness, especially after heat treatment.
• Processing: Cold rolling or heat treatments (e.g., quenching and tempering) can significantly increase hardness.

Let’s examine 1018 and 4140 steel to compare their hardness.

SAE-AISI 1018 Steel: Properties and Hardness

1018is a low-carbon steel known for its excellent machinability and weldability, commonly used in precision components.

• Chemical Composition: 0.15-0.20% carbon, 0.60-0.90% manganese, trace phosphorus and sulfur.
• Processing: Typically cold-rolled or cold-drawn, which slightly increases hardness compared to hot-rolled steel.
• Mechanical Properties:
  • Yield Strength: ~370 MPa (53,700 psi, cold-rolled).
  • Tensile Strength: ~440 MPa (63,800 psi).
  • Hardness: In its cold-rolled state, 1018 typically has a Brinell hardness (HB) of 126-197, depending on processing. In the annealed (softened) state, hardness is lower, around 126-150 HB.
• Heat Treatment: 1018 has limited hardenability due to its low carbon content. Carburizing (adding carbon to the surface) can increase surface hardness, but it’s not commonly hardened through quenching.
• Applications: Shafts, pins, fasteners, and machined parts where moderate strength and ease of machining are priorities.

SAE-AISI 4140 Steel: Properties and Hardness

4140is a low-alloy steel with higher carbon and alloying elements, designed for high strength and toughness, often used in demanding applications.

• Chemical Composition: 0.38-0.43% carbon, 0.75-1.00% manganese, 0.80-1.10% chromium, 0.15-0.25% molybdenum.
• Processing: Available in hot-rolled, cold-rolled, or heat-treated conditions (e.g., quenched and tempered).
• Mechanical Properties:
  • Yield Strength: ~415-655 MPa (60,000-95,000 psi, depending on heat treatment).
  • Tensile Strength: ~655-950 MPa (95,000-138,000 psi).
  • Hardness:
    • Annealed: ~197-237 HB.
    • Quenched and Tempered: Can reach 229-600 HB or 20-50 HRC, depending on tempering temperature. For example, tempering at 400°C yields ~40-45 HRC, while tempering at 600°C yields ~20-25 HRC.
• Heat Treatment: 4140’s higher carbon and alloy content (chromium, molybdenum) allow it to respond well to quenching and tempering, significantly increasing hardness and strength.
• Applications: Gears, crankshafts, tool dies, and heavy-duty machinery parts requiring high strength and wear resistance.

Hardness Comparison: 1018 vs. 4140

4140 steel is significantly harder than 1018 steel, especially when heat-treated. Here’s a detailed comparison:

• In Annealed Condition: 4140 (197-237 HB) is harder than 1018 (126-150 HB) due to its higher carbon and alloy content.
• In Heat-Treated Condition: 4140’s ability to achieve 229-600 HB (20-50 HRC) through quenching and tempering makes it far harder than 1018, which has limited hardenability.
• Cold-Worked 1018: Even cold-rolled 1018 (up to 197 HB) is generally softer than annealed 4140 and much softer than heat-treated 4140.

Why is 4140 Harder?

• Higher Carbon Content: 4140’s 0.38-0.43% carbon (vs. 1018’s 0.15-0.20%) allows for greater hardness, especially after heat treatment.
• Alloying Elements: Chromium and molybdenum in 4140 enhance hardenability, enabling significant hardness increases through quenching and tempering.
• Heat Treatment Response: 4140’s alloying makes it ideal for heat treatments that boost hardness, while 1018’s low carbon limits such effects.

Practical Implications

• Choose 1018for applications requiring easy machining, weldability, or cost-effectiveness, such as pins, fasteners, or non-critical components. Its lower hardness makes it less wear-resistant but easier to work with.
• Choose 4140for high-stress, wear-resistant applications like gears, dies, or crankshafts, where hardness and toughness are critical. Its higher cost and harder machining are trade-offs for superior performance.
• Comparison to A36: For context, ASTM A36/A36M (hot-rolled, 119-159 HB) is softer than both 1018 and 4140, suited for structural uses rather than precision or high-wear applications.

Why Choose Gangsteel?

While Gangsteel specializes in structural steels like ASTM A36/A36M and ASME SA 36 steel plate supplier, we can guide you in selecting the right steel for your needs, including 1018 or 4140 equivalents (e.g., Q235B, 42CrMo). Our services include:

• Quality Assurance: Compliance with ASTM, AISI, and international standards.
• Custom Solutions: Tailored steel forms for your project.
• Expert Support: Guidance on material selection for hardness, strength, or cost.

Conclusion: 4140 steel is significantly harder than 1018, especially when heat-treated, due to its higher carbon and alloy content. For projects requiring hardness and durability, 4140 is the better choice, while 1018 suits applications prioritizing machinability and cost. Contact Gangsteel for high-quality steel solutions and expert advice tailored to your project.